Thickeners for aqueous systems are needed for various purposes. For example, thickeners are used in latex paints to provide the desired viscosity and to stabilize emulsions and pigment dispersions. Thickeners are also used in the preparation of cosmetics and pigment pastes, textile manufacturing and in many processes that involve the treatment of water including oil drilling and enhanced oil recovery operations.
Hydroxyethyl cellulose is a conventional thickener for aqueous systems, but it has various deficiencies in that excessive amounts must be used and the rheology of the thickened system is often inadequate. Other conventional thickeners include polyacrylamide, polyvinyl pyrrolidone, polyvinyl alcohol and similar polymers. Various ethoxylated carboxyl-functional polymers which form alkali soluble thickeners are also known, but these also have various deficiencies, including inadequate hydrolytic stability.
U.S. Pat. No. 4,514,522 to Shay et al. describes alkali soluble latex thickeners that are particularly useful in increasing the viscosity and improving the rheology of a latex paint. Such thickeners, however, are somewhat sensitive to pH changes and high salt concentrations.
It has long been desired to provide superior thickeners for aqueous systems which are highly efficient, and which better resist hydrolysis and provide better rheology than conventional thickeners. It is particularly desirable to provide thickeners for aqueous systems having improved thickening efficiency over materials such as polyacrylamide and the like without the salt and pH sensitivities of the anionic thickeners described in the foregoing patent.